Evacuated elctron discharge tubes

ABSTRACT

An ion getter pump for providing a vacuum in a high power microwave discharge tube consists of a body of radio-active material which is arranged to act as the power source for the pump. The pump has a glass support base concentrically surrounding a cathode. Mounted within the tubular cathode is a layer of radio-active isotope material and a particle receiver from which extends an anode rod. Pins are fused through the base to support the cathode, the particle receiver and the isotope material. A shield is provided to prevent sputtering of material on to the base.

United States Patent [191 [111 7 3,786,296 Howorth Jan. 15, 1974 EVACUATED ELCTRON DISCHARGE TUBES Inventor: Jonathan Ross Howorth,

Chelmsford, England Foreign Application Priority Data May 15, 1970 Great Britain 23,6l9/7l U.S. CI. 313/176, 313/54 Int. Cl. H01j 19/70 Field of Search .L 313/54, 176

References Cited UNITED STATES PATENTS 8/l955 Batina 313/54 Primary Examiner-Roy Lake Assistant ExaminerDarwin R.- Hostetter Att0rneyBaldwin, Wight & Brown [57] ABSTRACT An ion getter pump for providing a vacuum in a high power microwave discharge tube consists of a body of radio-active material which is arranged to act as the power source for the pump. The pump has a glass support base concentrically surrounding a cathode. Mounted within the tubular cathode is a layer of radio-active isotope material and a particle receiver from which extends an anode rod. Pins are fused through the base to support the cathode, the particle receiver and the isotope material. A shield is provided to prevent sputtering of material on to the base.

27 Claims, 6 Drawing Figures F v 7 A I y N I g l r v I M 10 W PATENTEDJAH'ISIHN W 1 OF 2 3,786,286

INVENTOR BY I w Mm PAIENIEDJAN 15 m4 3. 786 296 SHEU 2 [IF 2 Hes e EVACUATED ELCTRON DISCHARGE TUBES This invention relates to evacuated electron discharge tubes. It is applicable to a wide variety of electron discharge tubes having envelopes in which, for satisfactory operation, a high degree of vacuum must be maintained. Though not limited to its application thereto it is particularly advantageous for microwave electron discharge tubes of high power.

Common practice with evacuated electron discharge tubes is to mount a chemically active getterin the envelope, which is pumped out to the desired high degree of vacuum and sealed. The useful life and performance of the tube depends upon maintenance of the vacuum, the vacuum tightness of the sealed envelope and the ability of the chemical getter to cope with gases generated in the tube while it is in use and in store, are relied upon to maintain the vacuum. Chemical getters are quite adequate in many cases but they are, of course, able to cope only with gases which react with the getter material but not with CH and inert gases generally. They are therefore not really adequate in some cases and the practice has developed of attaching getter ion pumps to the more expensive electron discharge tubes to. provide better maintenance of vacuum and thus extend the useful satisfactory life of the tube. A known getter ion pump, however, has the serious'practical disadvantage of requiring an external electric power supply for its operation. Moreover, the getter ion pump will affect pumping only when the external power supply is switched in not when the tube is merely in storage. The present invention seeks to avoid these disadvantages.

According to this invention an evacuated electron discharge tube apparatus comprises an electron discharge tube and an ion getter pumping device including a body of radioactive material arranged to act as the source of power therefor, said device being either within a vacuum tight housing constituted by the envelope of the tube or within a vacuum tight housing which includes the tube envelope, an envelope for said device and a communication channel between them.

The body of radio-active material may be an a particle source. Preferred examples of such materials are cm and Amm. If either of these materials is employed means are preferably associated therewith for reducing undesired accompanying X-ray emission therefrom. Such means may be constituted, for example, by thin mild steel sheet.

Instead of a source of a particles a source of B particles may be used for the body of radio-active material. A preferred source of B particles is Tritium preferably Tritium dissolved in Ti.

Preferably the pumping device is so constructed as to combine the action of an ion getter pump with that of a chemical getter.

In one form of apparatus in accordance with the invention the device has an enclosure comprising a support base and a hollow cathode, and a body of radioactive material, a collector and an anode are supported from said base in the interior of said cathode, said enclosure being such as to provide a free path for gas from the interior to the exterior thereof and the whole arrangement being such that emitted particles are confined within said enclosure. At least the interior surface of the cathode is preferably of chemical getter material, as also are, preferably, the collector and the anode. The

confining of emitted particles within the enclosure may be obtained by making the cathode and the base of particle-impermeable materials, forming them as structures open each at one end, and mounting them with their open ends overlapping, one within the other. Thus, for example, the cathode and the base may each be in the form of a hollow cylindrical structure of particle-impermeable material open at one end only, the two said structures being of different diameters and mounted co-axially with their open ends overlapping and one within the other to leave an annular space between them where they overlap.

In one construction of the device the cathode and the base are each in the form of a hollow cylinder open at one end only, the two cylinders being of different diameters and mounted co-axially with their open ends one within the other to leave an annular space between them, and the base supports the cathode cylinder and within the same, a source of 01 particles and a collector adjacent said source, there being an anode rod or wire which extends nearly to the closed end of the cathode cylinder and which is carried from the collector, a high resistance being connected between the collector and the a particle source, and a connection being provided between said source and said cathode cylinder.

In another construction of the device the cathode and the base are each in the form of a hollow cylinder open at one end only, the two cylinders being of different diameters and mounted co-axially with their open ends one within the other to leave .an annular space between them, and the base supports the cathode cylinder and within the same, a source of B particles and a collector adjacent said source, there being an anode rod or wire which extends nearly to the closed end of the cathode and which is carried from said source, a high resistance being connected between the collector and the B particle source, and a connection being provided between the collector and the cathode cylinder.

In both the aforesaid constructions the preferred ma terial for at least the interior of the cathode and also for the collector and the anode is Ti and a preferred material for the base is glass. Also, in both'said constructions a shield, e.g. of M0, is preferably provided for preventing the sputtering of metal on the base.

A further form of pumping device comprises an outer support with a thin layer of radio-active material on its inner surface, a co-axial anode, at least one co-axial grid between said anode and said support and a pair of shields, one at each end of the anode and co-axial support structure. In one construction of this nature the layer is an a particle source and there are two co-axial grids, the inner being connected to the source and to the shields and being a relatively transparent ioncollecting grid, and the outer being connected to the anode and being a relatively opaque a particle collecting grid. In another construction the layer is a [3 particle source and there is only one grid which is connected to the shields, is operated at a negative potential and is a B particle collecting grid. In both these constructions electrons orbit around the central anode to cause ionisation.

The invention is illustrated in the accompanying drawings in which FIGS. I and 2 are, respectively, a diagrammatic sectional elevation and a diagrammatic sectional plan of one form of pumping device for an apparatus in accordance with this invention; FIGS. 3 and 4 are views, respectively similar to those of FIGS. 1 and 2 of a modified form of pumping device having rather better disposition of the radio-active material; FIG. is a view showing one type of envelope construction; and FIG. 6 is a view showing another type of enevelope construction.

The pump shown in the drawings is adapted to act both as what may be termed a radio getter pump, that is to say a getter pump which is powered by a radioactive isotope, and as a chemical getter. Referring to the drawings, 1 is a glass support base and 2 is a cathode in the form of a cylindrical can open at one end. A layer of radioactive isotope material 3 on a support backing plate 4, and a particle receiver 5 from which extends an anode wire or rod 6 are supported from the base in the interior of the cathode. The base 1 is also shaped as a cylinder, open at one end. It is co-axial with the cathode, is of larger diameter than said cathode and its open end overlaps, is spaced from and surrounds the open end of the cathode. Support pins 7 fused through the base 1, support the cathode 2 and similarly fused-in support pins 8 and 9 support the backing plate 4 and the particle receiver 5 with its anode rod 6. A shield 10, also supported by the pin 9, is provided to prevent sputtering of metal on to the base 1. A high resistance 11, which does not appear in FIG. 2, connects, through the pins 8 and 9, the parts 4 and 5, and a connection 12, which also does not appear in FIG. 2, connects the parts 4 and 2 through the pin 8 and one of the pins 7. To quote a practical figure by way of example only the value of resistance 11 could be l0 ohms. At least the inner surface of the cylinder 2 may be made of a material such as Ti, Ta or Zr which is a satisfactory getter when in the form of a freshly sputtered layer. The said cylinder 2 could be made entirely of such material or it could be of any suitable material with a sputtered layer of such getter material on its inner surface. At present Ti is preferred. The particle receiver 5, and the anode rod 6 are all also of getter material, eg all of Ti. The isotope backing plate 4 may be of any suitable material, e.g., Al and the shield 10 may be of, for example, Mo.

Preferably the isotope layer 3 is of a radioactive material emitting 11 particles. Preferably also it is a radioactive material which is very low in 'y ray emission. There are three well known isotopes which comply with these requirements, namely Po Cm and Am the first named having a 'y ray emission of only about 0.001 percent. However, this material has the defect of being volatileand the other two materials are therefore at present preferred. They both emit low energy X-rays but it is possible to reduce the X-ray count substantially by the use of X-ray protective material (not shown). Experiment indicates that it is possible, by the use of lmm thick sheet steel, to reduce the X-ray count to about 0.1 percent of the a emission rate.

Considerations of human protection against physiologically damaging radiation place a practical limit on the size of the a particle source 3 which can be employed for it must be assumed that human beings will be for long periods within radiation range of a discharge tube apparatus in accordance with this invention. Safety regulations at present prohibit continuous exposure to more than 300m. Rad/week. This is equivalent to 2m.Rad/hour for a man sitting continuously by a vacuum tube with a radio getter pump inside it. This corresponds to 10 disintegrations/sec. for SOKeV. y rays. If 0.1 percent y rays are emitted, the maximum size of a source would be 10' disintegrations/sec. 2 curie.

With a device of the construction and arrangement above described with reference to the drawings, the a particles will be confined to the interior of the device, the glass base 1 and cathode can 2, overlapping as shown, being of a particle impermeable material and sufficient to accomplish this. If, however, a different construction which does not in itself achieve this is adopted e.g., if a base made of a particle permeable material is used any known suitable external shielding (not shown) may be used to prevent escape of 0: particles away from the interior of the pump.

Because an a particle carries two positive electric charges an a particle source constitutes a substantially constant current source and if such a source (the layer 3 in the illustrated embodiment) is separated from a collector (the collector 5) by a sufficiently high resistance (the resistance 11), a high voltage can be built up. This voltage is used, when the pump is in operation, as driving voltage for providing pumping action after the manner of an electro-static ion pump.

The device illustrated is adapted to provide pumping in three ways namely by chemical pumping, pumping by ionisation by a particles and electrostatic pumping as by an electrostatic ion pump. If one assumes a radioactive source giving approximately l0 disintegrations/sec., a resistance 11 of 10 ohms and a built-up voltage of 10 volts, the receiver 5 will be bombarded by 10 particles/sec and if one percent of this sputters new atoms available for chemical reaction with gas molecules, chemical gettering may be expected to remove 10 mols/sec. which is equivalent to 10 torr.l/sec; pumping by ionisation by (1 particles may be expected also to approach 10 torr.l/sec; and electrostatic pumping by further ionisation by electrons supplied by the ionising effect of the 0: particles may be expected to approach a further 10 torr.l//sec: making a total expected approximate pumping speed 10" 10 10 torr.l/sec. Of course when the supply of ions becomes greater than the current produced by the a particles no ion pumping will occur. If one assumes a device of the foregoing performance to be fitted in or in communication with a discharge tube envelope of 1' litre volume and initially at 10" torr, the pressure may be expected to reduce to 10 torr. in about 4 days and in about a week the tube may be expected to reach and maintain an equilibrium pressure which will depend on the rate of outgassing of the electrodes and other components inside the tube envelope.

The invention is not limited to the use of radioactive materials emitting a particles and materials emitting B particles e.g., Tritium dissolved in Ti may be used instead. B particles would not sputter atoms from the collector and since such particles are negatively charged, the parts 5 and 3 of the illustrated embodiment would have to be interchanged if a B particle source is used instead of an a particle source. Because of the reduced sputtering obtained with a B particle source, a device employing such a source would (other things being equal) have a lower pumping speed than one employing an a particle source. On the other hand, some B particle sources do not emit 'y rays, and, by selecting such a source, 'y ray emission can be obviated.

FIGS. 3 and 4 are views, similar respectively to those of FIGS. 1 and 2 of another form of pumping device for an apparatus in accordance with this invention. This tral anode.

modified form of device has the advantage of providing a large area radioactive source. Both a and B sources work most efficiently when in thin film form and in many cases, therefore, large area sources are desirable.

In FIGS. 3 and 4 an a particle source is constituted by a thin film 33 of suitable radioactive material on the inner surface of an openended cylindrical support backing member 44 which co-axially surrounds an anode rod 66. A glass base disc 101 (not shown in FIG. 3) supports, directly or indirectly, the parts 33, 44 and 66 and also two end shields 110 (not shown in FIG. 3)

as well as two co axial cylindrical grids l3 and 14 of different diameters between the parts 66 and 33 44. The outer grid 14 may be fairly opaque and designed to collect, say, about 70 percent of the 0: particles. The inner grid 13 is intended to collect ions and may be relatively transparent. The outer grid 14 and the anode 66 are connected together and operated at a suitable positive potential. The inner grid 13, the source 33 with its backing support 44 and the shields 110 are connected together. This pumping device operates after the manner of a so-called orbitron in the sense that electrons can orbit or circulate indefinitely around the central anode 66, thus causing ionisation. .A high resistance 11 connectsthe anode with the inner grid.

FIGS. 3 and 4 show a pump device with an a particle source. In the case where a B particle source is required a design, generally like that of FIGS. 3 and 4 (but not illustrated) could be used, differing, however, from that of FIGS. 3 and 4 in that there would be only a single grid between the central anode and the radio-active material (now, of course, a B particle source) on the inside of the cylindrical support. This grid would be thick, designed to collectmost of the B particles, be held at negative potential, and be connected to the end shields. The anode rod and the [3 particle source would be operated at positive potential. As before electrons would,in operation, orbit or circulate around the cen- As noted, the'getter device may be housed within the electron discharge tube envelope or it may have its own envelope communicating with that of the tube. In FIG. 5, the getter device G is shown housed within the. envelope E which also houses the components (not shown) of the electron'discharge tube. In FIG. 6, the getter device G is housed within an envelope e which, through the channel C, communicates with the interior of the electron discharge tube envelope E.

I claim: 1. For use in combination with an electron discharge tube having an envelope defining an evacuated space, an ion getter pumping device of hollow interior form communicating with said evacuated space and tending to establish an equilibrium pressure within said space, said pumping device comprising:

means for defining said hollow interior; anode means within said hollow interior; particle collector means within said hollow interior; a source of radio-active material within said hollow interior and spaced from said collector means;

cathode means within said hollow interior and spaced from said anode means, said anode means and said cathode means being provided with electrical connector means for establishing an electrical potential therebetween when the electron discharge tube is in operation; and

resistance means electrically connecting said source and said collector means for establishing a high voltage potential therebetween independently of electron discharge tube operation to effect ion getter pumping action even when the electron discharge tube is not in operation.

2. An ion getter pumping device as defined in claim 1 wherein said device is housed within the envelope of the associated electron discharge tube. g

3. An apparatus as claimed in claim 1 wherein the source of radio-active material is an a particle source.

4. An apparatus as claimed in claim 3 wherein the particle source is Cm 5. An apparatus as claimed in claim 3 wherein the particle source is Am 6. An apparatus as claimed in claim 4 wherein there is associated with the particle source means for reducing undesired accompanying X-ray emission therefrom.

7. An apparatus as claimed in claim 6 wherein the X-ray reducing means is constituted by mild steel sheet.

8. An apparatus as claimed in claim 1 wherein the source of radio-active material is a [3 particle source.

9. An apparatus as claimed in claim 8 wherein the particle source is Tritium.

10. An apparatus as claimed in claim 1 wherein the pumping device is so constructed as to combine the action of an ion getter pump with that of a chemical, getter. 1

I 11. An apparatus as claimed in claim 1 wherein said cathode means comprises a hollow cathode and including a support base cooperating with said hollow cathode to form said means for defining a hollow interior, said collector means and said anode means being supported from said base in the interior of said hollow cathode, and the whole arrangement being such that emitted particles are confined within said hollow interior.

12. An apparatus as claimed in claim 11 wherein the interior surface of the hollow cathode is of chemical getter material.

13. An apparatus as claimed in claim 12 wherein the interior surfaces of the'collector means anti anode means are also of chemical getter material. I

14. An apparatus as claimed in claim 11 wherein the confining of emitted particles within the hollow interior is obtained by making the hollow cathode and the base of particle-impermeable materials, forming them as structures open each at one end, and mounting them with their open ends overlapping, one within the other.

15. An apparatus as claimed in claim 14 wherein the hollow cathode and base are each in the form of a hollow cylindrical structure of particle-impermeable material open at one end only, the two said structures being of different diameters and mounted co-axially with their open ends overlapping and one within the other to leave an annular space between them where they overlap.

16. An apparatus as claimed in claim 11 wherein the hollow cathode and the base are each in the form of a hollow cylinder open at one end only, the two cylinders being of different diameters and mounted co-axially with their open ends one within the other to leave an annular space between them, and the base supports the cathode cylinder and within the same, said source in which the radioactive material is a source of 0: particles and said collector means disposed adjacent said source, said anode means being in the form of a rod or wire which extends nearly to the closed end of the cathode cylinder and which is carried from the collector means.

17. An apparatus as claimed in claim 11 wherein the hollow cathode and the base are each in the form of a hollow cylinder open at one end only, the two cylinders being of different diameters and mounted co-axially with their open ends one within the other to leave an annular space between them, and the base supports the cathode cylinder and within the same, said source being a source of [3 particles and said collector means being adjacent said source, said anode means being in the form of an anode rod or wire which extends nearly to the closed end of the cathode cylinder and which is carried from said source.

18. An apparatus as claimed in claim 16 wherein the material for at least the interior of the cathode cylinder and also for the collector means and the anode means is Ti.

19. An apparatus as claimed in claim 17 wherein the material for at least the interior of the cathode cylinder and also for the collector means and the anode means is Ti.

20. An apparatus as claimed in claim 16 wherein the material for the base is glass.

21. An apparatus as claimed in claim 17 wherein the material for the base is glass.

22. An apparatus as claimed in claim wherein a shield is provided for preventing the sputtering of metal on to the base.

23. An apparatus as claimed in claim 1 wherein said means for defining a hollow interior comprises an outer cylindrical support with a thin layer of radioactive material on its inner surface and a pair of shields, one at each end of the cylindrical support, said anode means being co-axial within said support, and at least one coaxial grid between said anode means and said cylindrical support.

24. An apparatus as claimed in claim 23 wherein said source is an a particle source and there are two co-axial grids, the inner being connected to the source and to the shields and being a relatively transparent ioncollecting grid, and the outer being connected to the anode and being a relatively opaque a particle collecting grid.

25. An apparatus as claimed in claim 23 wherein said source is a ,8 particle source and there is only one grid which is connected to the shields, is operated at a negative potential and is a B particle collecting grid.

26. An apparatus as claimed in claim 8 wherein the particle source is Tritium dissolved in Ti.

27. An ion getter pumping device as defined in claim 1 including an envelope housing said device separate from but communicating with the envelope of the associated electron discharge tube.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 786,296 Dated January 15, 1974 Inventor(s) JOnathan ROSS HOwOrth It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Please change "Assignee: English Electric Company Limited" to -Assignee: English Electric Valve Company Limited-.

Signed and Sealed this Arrest:

RUTH C. MASON Alresring Officer C. MARSHALL DANN (mnmissinnor of Parents and Trademarks F ORM PO-105O (10-69) USCOMM-DC 5O376-P69 U,S. GOVERNMENT PRINTING OFFICE I I959 O-356-334, 

1. For use in combination with an electron discharge tube having an envelope defining an evacuated space, an ion getter pumping device of hollow interior form communicating with said evacuated space and tending to establish an equilibrium pressure within said space, said pumping device comprising: means for defining said hollow interior; anode means within said hollow interior; particle collector means within said hollow interior; a source of radio-active material within said hollow interior and spaced from said collector means; cathode means within said hollow interior and spaced from said anode means, said anode means and said cathode means being provided with electrical connector means for establishing an electrical potential therebetween when the electron discharge tube is in operation; and resistance means electrically connecting said source and said collector means for establishing a high voltage potential therebetween independently of electron discharge tube operation to effect ion getter pumping action even when the electron discharge tube is not in operation.
 2. An ion getter pumping device as defined in claim 1 wherein said device is housed within the envelope of the associated electron discharge tube.
 3. An apparatus as claimed in claim 1 wherein the source of radio-active material is an Alpha particle source.
 4. An apparatus as claimed in claim 3 wherein the particle source is Cm242.
 5. An apparatus as claimed in claim 3 wherein the particle source is Am241.
 6. An apparatus as claimed in claim 4 wherein there is associated with the particle source means for reducing undesired accompanying X-ray emission therefrom.
 7. An apparatus as claimed in claim 6 wherein the X-ray reducing means is constituted by mild steel sheet.
 8. An apparatus as claimed in claim 1 wherein the source of radio-active material is a Beta particle source.
 9. An apparatus as claimed in claim 8 wherein the particle source is Tritium.
 10. An apparatus as claimed in claim 1 wherein the pumping device is so constructed as to combine the action of an ion getter pump with that of a chemical getter.
 11. An apparatus as claimed in claim 1 wherein said cathode means comprises a hollow cathode and including a support base cooperating with said hollow cathode to form said means for defining a hollow interior, said collector means and said anode means being supported from said base in the interior of said hollow cathode, and the whole arrangement being such that emitted particles are confined within said hollow interior.
 12. An apparatus as claimed in claim 11 wherein the interior surface of the hollow cathode is of chemical getter material.
 13. An apparatus as claimed in claim 12 wherein the interior surfaces of the collector means and anode means are also of chemical getter material.
 14. An apparatus as claimed in claim 11 wherein the confining of emitted particles within the hollow interior is obtained by making the hollow cathode and the base of particle-impermeable materials, forming them as structures open each at one end, and mounting them with their open ends overlapping, one within the other.
 15. An apparatus as claimed in claim 14 wherein the hollow cathode and base are each in the form of a hollow cylindrical structure of particle-impermeable material open at one end only, the two said structures being of different diameters and mounted co-axially with their open ends overlapping and one within the other to leave an annular space between them where they overlap.
 16. An apparatus as claimed in claim 11 wherein the hollow cathode and the base are each in the form of a hollow cylinder open at one end only, the two cylinders being of different diameters and mounted co-axially with their open ends one within the other to leave an annular space between them, and the base supports the cathode cylinder and within the same, said source in which the radioactive material is a source of Alpha particles and said collector means disposed adjacent said source, said anode means being in the form of a rod or wire which extends nearly to the closed end of the cathode cylinder and which is carried from the collector means.
 17. An apparatus as claimed in claim 11 wherein the hollow cathode and the base are each in the form of a hollow cylinder open at one end only, the two cylinders being of different diameters and mounted co-axially with their open ends one within the other to leave an annular space between them, and the base supports the cathode cylinder and within the same, said source being a source of Beta particles and said collector means being adjacent said source, said anode means being in the form of an anode rod or wire which extends nearly to the closed end of the cathode cylinder and which is carried from said source.
 18. An apparatus as claimed in claim 16 wherein the material for at least the interior of the cathode cylinder and also for the collector means and the anode means is Ti.
 19. An apparatus as claimed in claim 17 wherein the material for at least the interior of the cathode cylinder and also for the collector means and the anode means is Ti.
 20. An apparatus as claimed in claim 16 wherein the material for the base is glass.
 21. An apparatus as claimed in claim 17 wherein the material for the base is glass.
 22. An apparatus as claimed in claim 15 wherein a shield is provided for preventing the sputtering of metal on to the base.
 23. An apparatus as claimed in claim 1 wherein said means for defining a hollow interior comprises an outer cylindrical support with a thin layer of radioactive material on its inner surface and a pair of shields, one at each end Of the cylindrical support, said anode means being co-axial within said support, and at least one co-axial grid between said anode means and said cylindrical support.
 24. An apparatus as claimed in claim 23 wherein said source is an Alpha particle source and there are two co-axial grids, the inner being connected to the source and to the shields and being a relatively transparent ion-collecting grid, and the outer being connected to the anode and being a relatively opaque Alpha particle collecting grid.
 25. An apparatus as claimed in claim 23 wherein said source is a Beta particle source and there is only one grid which is connected to the shields, is operated at a negative potential and is a Beta particle collecting grid.
 26. An apparatus as claimed in claim 8 wherein the particle source is Tritium dissolved in Ti.
 27. An ion getter pumping device as defined in claim 1 including an envelope housing said device separate from but communicating with the envelope of the associated electron discharge tube. 